MECHANICAL ENERGIES OF THE SOLAR SYSTEM. 77 



probably as insensible, in comparison with the heat of friction, as it has been 

 shown the heat of any combustion or chemical action they can experience must be, 

 or as we have tacitly assumed the heat is which is taken and kept by the meteors 

 themselves in approaching from cold space to lodge permanently in the Sun. We 

 may conclude that the Sun's heat is caused, not by solids striking him, or darting 

 through his atmosphere, but by friction in an atmosphere of evaporated meteors, 

 drawn in and condensed by gravitation while brought to rest by the resistance of 

 the Sun's surface. The quantity of meteoric matter required, if falling in solid, 

 would, as we have seen, be such that half the work done by Solar Gravitation on 

 it in coming from an infinite distance, is equal to the energy of heat emitted from 

 the Sun, and would, therefore, amount to a pound every 2 3 hours per square foot 

 of the Sun's surface ; and it will be the same as this, notwithstanding the pro- 

 cess of evaporation and condensation actually going on, if, as appears probable 

 enough, the velocity of the vortex of vapour immediately external to the region 

 of intense resistance in all latitudes be nearly equal to that of a planet close to 

 the Sun. 



No. III. On the Distribution of Temperature over the Sun's Surface. 



Not only the larger planets, but the great mass of meteors revolving round the 

 Sun, appear to revolve in planes nearly coinciding with his equator, and there- 

 fore such bodies, if solid when drawn in to the Sun, would strike him principally 

 in his equatorial regions, and would cause so much a more copious radiation of 

 heat from those regions than from any other parts of his surface, that the ap- 

 pearance would probably be a line or band of light, instead of the round, bright 

 disc which we see. The nearly uniform radiation which actually takes place from 

 different parts of the Sun's surface appears to be sufficiently accounted for by the 

 distillation of meteors, which, we have seen, must, in all probability, take place 

 from an external region of evaporation at a considerable distance (perhaps several 

 times his radius) inwards to his surface where they are condensed. Whatever 

 be the dynamical condition of the luminous atmosphere of intense resistance, it 

 is clear that there must be a very strong tendency to an equality of atmospheric 

 pressure over the probably liquid surface of the Sun, and that the temperature 

 of the surface must be everywhere kept near that of the physical equilibrium be- 

 tween the vapours and the liquid or solid into which they are distilling. A lower- 

 ing of temperature in any part would therefore immediately increase the rate of 

 condensation of vapour into it, and so bring a more copious influx of meteoric 

 matter with dynamical energy to supply the deficiency of heat. The various 

 deviations from uniformity which have been observed in the Sun's disc are pro- 

 bably due to eddies which must be continually produced throughout the 

 atmosphere of intense resistance between his surface (which at the equator 

 revolves only at the rate of 13 miles per second) and the great vortex of meteoric 



